It is usual, particularly in the aforesaid application, to measure the temperature prevailing inside an oven by means of an optical pyrometer. Such an instrument enables the temperature of a body (wafers to be treated) to be determined by analysing the radiation emitted by the latter without any physical contact with the body itself.
However, pyrometers are subject to loss of adjustment and/or drift particularly as a function of the number of measurements made. Up till now, in order to recalibrate such a pyrometer, a reference thermocouple was fixed to the upper face of a wafer placed in an oven and the pyrometer was recalibrated so that the readings given by the thermocouple and those given by the pyrometer coincide.
Such a calibration method has many drawbacks, the most significant of which is that it requires the installation of a thermocouple in the oven, with its electrical connections to the means for processing the signals. In the majority of applications, it is essential for the objects treated (the wafers) to be treated without any contamination and therefore without any handling. However, introducing the thermocouple into the treatment oven and passing the electrical connections through are contamination factors. Moreover, the thermocouple wires must be soldered to the wafer by means of soldering carried out with a material different from that of the wafer. Because of this, the temperature reading given by the thermocouple has an error inherent in the nature and form of the soldering. This error, which is difficult to predict, cannot be corrected in a reproducible manner.
The objective of the present invention is to mitigate all these drawbacks by providing a method and device for calibrating an optical pyrometer which do not require the introduction of any foreign bodies into the oven and allow in situ calibration of the pyrometer.